The present invention relates to a torsional vibration insulator for a vehicle drive train.
In vehicles having an internal combustion engine, torsional vibrations occur in the drive train due to the intermittent operating mode of the engine. Dual-mass flywheels, usually situated between the engine and the transmission input, have been used for quite some time to “insulate” and damp these torsional vibrations. Such a dual-mass flywheel is known from DE 197 00 851 A1 and DE 195 22 718 A1, for example.
Dual-mass flywheels, explained in a very simplified manner, comprise a primary element and a secondary element which can rotate relative to one another about a rotational axis. Multiple helical spring-like spring elements are circumferentially distributed between the primary element and the secondary element in a circumferential direction of the rotational axis. The spring elements have an arc-shaped curvature in the circumferential direction, and are therefore also referred to as “bow springs.” The arc-shaped spring elements are pressed together during a relative rotation of the primary element with respect to the secondary element.
In the radial direction, each bow spring is supported from the outside by a “shell-like recess,” such as a support plate, provided on the primary element or on the secondary element. This prevents the bow springs from “yielding” radially outward when pressed together. Frictional forces arise between the bow springs and the recesses or plate shells which support the bow springs in the radial direction. The frictional forces are attributed to the fact that the bow springs have an arc-shaped curvature in the circumferential direction, and the supporting forces acting on the ends of the bow springs are not aligned, but, rather, intersect one another at a certain angle, producing a resultant radial force on the bow spring. This causes a dual-mass flywheel to rotate at a high rotational speed, thereby generating centrifugal forces which act in the radial direction and press the bow springs farther outward.
Tests have shown that the torsional rigidity of a dual-mass flywheel in dynamic operation (high rotational speed) is up to 40 times greater than when in static operation (standstill or low rotational speed), which is attributed primarily to the centrifugal forces acting on the bow springs and the frictional forces thus produced. At high rotational speeds it is observed that, when torque is relieved on the dual-mass flywheel, as a result of the centrifugal force friction itself the bow springs remain “stuck” to the friction shells or recesses which support them in the radial direction, and do not correspondingly relax when the torque is relieved, but instead relax abruptly only when the rotational speed drops, temporarily causing an undesired play in the drive train. This leads to oscillation problems such as transmission rattling, thrust humming, or general overall vibrations. To avoid these problems and to reduce the wear between the bow springs and the friction shells or recesses in which the bow springs are situated, the recesses are often filled with lubricating grease, which mitigates the above-mentioned problems but does not eliminate them.
An object of the invention is to provide a torsional vibration insulator in which the above-referenced problems are avoided.
The invention proceeds from a torsional vibration insulator for a drive train of a vehicle. The torsional vibration insulator comprises a primary element and a secondary element which can rotate relative to one another about a rotational axis. The primary element forms the “torque input,” and the secondary element forms the “torque output,” of the torsional vibration insulator. In addition, at least two “spring elements” are provided which extend in an arc in a circumferential direction of the rotational axis. The spring elements may be formed by helical springs, which are also known as “bow springs” on account of their curvature in the circumferential direction. The spring elements or bow springs are each supported on a radial outer face by a “radial support device.” In the circumferential direction a first end of each spring element is supported by the primary element, and a second end of each spring element is supported by the secondary element. The length of the spring elements, viewed in the circumferential direction, is modifiable by rotating the primary element with respect to the secondary element. “Modifiable” means that the spring elements are pressed together in a relative rotation of the primary element with respect to the secondary element.
A key concept of the invention lies in the design of the radial support devices, which prevent radial “yielding” of the spring elements when the arc-shaped spring elements are pressed together. The radial support devices according to the invention have multiple support elements that engage with the radial outer face of the spring elements. The support elements are rotatably mounted in the circumferential direction. In this context, “rotatably” means that the support elements can be carried along with the spring elements in the circumferential direction when the length of the spring elements is modified, i.e., when the primary element is rotated relative to the secondary element.
In contrast to customary configurations in which compression and relaxation of the bow springs produces a relative motion of the bow springs with respect to the friction plates or recesses which radially support the bow springs, according to the invention such a relative motion is avoided. Thus, the friction problems on the bow springs and the friction shells or recesses in which the bow springs are mounted and radially supported, which occur more frequently with conventional torsional vibration insulators, in particular at higher rotational speeds, are completely avoided. Greasing of the bow springs may be omitted in a configuration according to the invention. Thus, by use of the invention a compression and relaxation of the bow springs that is substantially free of reaction forces is achieved which corresponds to the instantaneously transmitted torque. The rotational speed of the torsional vibration insulator therefore has practically no effect on the compression and relaxation response of the bow springs.
The support elements may be U-shaped or bracket-shaped, for example, and radially enclose the spring elements (bow springs) from the outside in a bracket-like manner. The support elements may be formed by plates bent in the shape of a U.
According to one refinement of the invention, two or more of the support elements provided are connected to one another via a shared holding element situated on the rotational axis. A first of these support elements is associated with the first spring element or the first bow spring, and a second of these support elements is associated with the second spring element or the second bow spring. The two support elements are connected to one another via the holding element in such a way that the radial supporting forces acting on the support elements in the holding element cancel out one another.
Preferably, each of the support elements is connected to the associated spring element in a friction-fit manner, thus protecting it from slippage in the circumferential direction. When the spring elements are helical springs, each of the support elements may be placed from the outside on individual windings of the helical springs. To avoid slippage of the support elements, windings of the helical springs may engage with a friction fit in recesses or grooves provided in the individual support elements.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.